1. Field of the Invention
The present invention relates to an optical lens system for taking image, and more particularly to a miniaturized optical lens system for taking image used in digital cameras, mobile phones or PDA products.
2. Description of the Prior Art
With the miniaturization of digital cameras, mobile phones and PDA products, the inner optical lens system for taking image is required to be miniaturized as much as possible. And the development of an image sensor such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) used in an optical lens system for taking image is toward the miniaturization and high resolution field. Therefore, an optical lens system in the future must satisfy the requirement of miniaturization and high resolution.
If the size of an optical lens system is miniaturized, and it must insert a glass cover and an IR Cut filter in the optical lens system, causing difficulty in ensuring a necessary back focal length, and the total optical length of the optical lens system will be too long. Further, when the total optical length of an ordinary optical lens system is shortened, the characteristic of an incident angle of the optical lens system will get worse.
Therefore, JP Pat. Nos. 2005-004045, 2005-227755, 2005-345919, 2005-352206, 2006-106321, 2006-133270 and 2006-163340 disclosed several improved projects, which adopt lens elements for taking image smaller than usual lens elements, and the aperture stop is located at the object side, so that the exit pupil of the optical lens system will be far away from the image plane. A three-piece lens system that can ensure a good characteristic of an incident angle and is made of plastic material and has aspheric shape with inflection point.
The disadvantages of the abovementioned projects lie in:
The magnification of the JP Pat. No. 2005-004045 is as great as 1.35˜1.48 (magnification is the ratio of the focal length to the entire optical length), which restricts the design for miniaturization.
JP Pat. No. 2005-227755 also ensures a back focal length, and the magnification is 1.19, which satisfies the requirement of miniaturization, but the field of view is as small as 58 degrees.
The magnification of the JP Pat. No. 2005-345919 is as great as 1.35˜1.48
The magnification of the JP Pat. No. 2005-352206 is as great as 1.38.
The product of the JP Pat. No. 2006-106321 satisfies the requirement of miniaturization, but the field of view as small as 58 degrees.
The product of the JP Pat. No. 2006-133270 satisfies the requirement of miniaturization, but the Fno is 3.85, so that the resultant brightness is relatively low.
The product of the JP Pat. No. 2006-163340 will produce a magnification as great as 1.3.
In view of abovementioned conventional projects, the present invention developed a product that satisfies the requirement of miniaturization and produces a smaller magnification by using only three lens elements to ensure the field of view.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.